1. Field of the Invention
This invention relates to film-forming polymer emulsions and processes for producing such polymer emulsions.
2. Description of the Prior Art
Film-forming polymer emulsions having a soft first stage and hard final stage are well known; for example, see Victorius U.S. Pat. No. 3,454,516. The use of coalescent in the final formulation of film-forming polymers, for example in paints, lacquers, coatings, and the like, is also known.
Prior film-forming polymer emulsions provide good properties, but even further improvements in the balance between minimum filming temperature (MFT) and early block resistance/high temperature hardness had been desired. It is known that increasing T.sub.g increases early block resistance and high temperature hardness of polymeric films, but prior artisans were limited as to T.sub.g because of MFT, i.e., if the T.sub.g was increased, the polymer would not form a film at ambient temperature, unless undesirably high levels of coalescent were added. It has not been possible up to now to achieve ambient temperature film-forming and superior early block resistance and high temperature hardness from a polymer emulsion containing a low level of coalescent.